Thermo-optic behaviour of water, ethanol and glycerol: Implications for photonic applications

Department of Physics, Dr. Vishwanath Karad MIT World Peace University (MIT WPU), Survey No. 124, Ex Servicemen Colony, Paud Road, Kothrud, Pune - 411038, India

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Published online: 26 June 2026

Abstract

We have measured refractive indices of water, ethanol and glycerol in the temperature range 25-50 oC using the digital Abbe refractometer attached with a recirculating water chiller. Based on these observations, some important thermo-optic parameters such as mean molecular polarizability, polarizability density, optical dielectric constant are calculated. The temperature coefficients of these parameters are also estimated. It is observed that all parameters except mean molecular polarizability show a systematic decrease with temperature. The analysis also indicates that water is maximally stable against thermo-optic variations, ethanol is maximally sensitive, while glycerol has intermediate response. Remarkably, the mean molecular polarizability shows a nonlinear thermal dependence. We have attempted to interpret all these observations using macroscopic as well as microscopic behaviour of water, ethanol and glycerol. The results in this study clearly suggest applications of water, ethanol and glycerol in liquid-based-photonic-systems such as fiber-optic temperature sensors, tunable optical components, and thermo-optic modulators.